What does failing to replace a defective thermostat in an engine usually result in?

Failing to replace a defective thermostat in an engine typically leads to engine overheating or underheating because the thermostat regulates the flow of coolant through the engine. When the thermostat is stuck closed, it prevents coolant from circulating, causing the engine to overheat. Conversely, if it is stuck open, the engine may not reach its optimal operating temperature, leading to underheating. Both scenarios can cause significant damage over time, including warped cylinder heads or poor fuel combustion, which impacts overall engine performance. Understanding the role of the thermostat emphasizes the importance of maintaining engine components to ensure they function properly and help avoid costly repairs or performance issues.